I'm addicted to a site called tvtropes.org. It's basically a catalogue of various literary and artistic devices used in various forms of media (books, movies, TV). It's fun because the site gives names to practices that you already recognize but haven't bothered to identify in any specific way. Examples include Genre Blindness, which explains the tendency of Bond villains to reveal their entire master plan to the spy rather than just shooting him, and Lampshading, which is an attempt to diffuse an obvious plot hole by having a character draw attention to it.
Another one of these articles is called "Darker and Edgier", which describes a "a Tone Shift that seeks to make a work of fiction 'more adult'." This should be familiar to anyone who has seen a recent superhero or science fiction movie. Christopher Nolan's Dark Knight trilogy, for example, is a grittier version of Tim Burton's Batman - which is itself a much grittier version of the awesome campfest that was the 1960's Batman TV show. Battlestar Galactica is another notorious example - it's a remake of the campy 1970's TV show and is, at times, extremely depressing.
Some people like these tone shifts, others don't. There is a certain kind of person who enjoys the campiness of the original Batman, and who does not think that the extreme angst of the new Battlestar Galactica counts as entertainment. That being said, I think most people do like the newer stuff better - a Batman movie similar in tone to the 1966 version would not, I suspect, have done nearly as well as Batman Begins).
Myself, I think I'm somewhere in the middle. I think that angst for the sake of angst is silly, but at the same time I think that people sometimes confuse "more realistic" and "more naturalistic" for "darker". I don't think they're the same thing, though they're often conflated.
For example, beyond a certain aesthetic that made the movie literally dark in colour, I don't actually consider Batman Begins to be a particularly dark movie in tone. The hero wins out in the end and the bad guys are defeated. What the movie did try to do was to make the character of Batman semi-plausible. The movie tries to answer certain questions about the character that most interpretations ignore. Why did Bruce Wayne become a costumed vigilante rather than D.A. or a police officer? Where did train? Where did he get his equipment? Why did he choose a bat as his personal symbol?
It goes further than that. The movie shows Batman getting hurt on numerous occasions. His expertise at martial arts, while impressive, isn't over the top. The cumulative effect is that Christopher Nolan's Batman is very much a three dimensional human being - more so than any other interpretation I can think of.
From what I can see in the trailer, the new Superman movie, Man of Steel, has a similar kind of vibe. To be sure, Superman isn't a realistic character, but the movie seems to be going to some length to make everything else around him seem real. Like Batman Begins, the movie seems to be asking questions that other interpretations gloss over. How does a real, honest-to-goodness superpowered alien manage to keep sane when he can hear everything? How would the world react to his existence? Nobody really knows, but prepping the military for an extraterrestrial invasion doesn't seem too far off the mark.
Some people take issue with this trend. One guy I work with, for example, is vagely irritated that James Bond in Skyfall is given a (relatively sparse) backstory. He's not interested in making his heroes more human. His heroes are abstract, and beyond the reach of mere distractions like backstory.
I, on the other hand, like this trend. I'm one of those guys who thinks that emphasizing a hero's humanity enhances his or her heroism rather detracts from it. One has a hard time relating to a mere abstraction. But when the hero is a three dimensional human being, when you can relate to him (or her), you have a greater sense that this kind of heroism is possible. One doesn't believe that Tim Burton's Batman is real. One could believe, for a split second, that Christopher Nolan's Batman is real, and that makes all the difference.
Of course, if you want dark - truly dark, as opposed to just realistic - well, there are plenty of examples of that too. The reboot of Battlestar Galactica is exceptionally dark, as befitting the subject matter (virtually the entire is human race wiped out, with the survivors being doggedly and ruthlessly pursude by the parties responsible). Watchmen is another example - with scenes including a pregnant woman being gunned down and New York City being destroyed, you know what kind of movie you're in for. The Walking Dead is pretty depressing, which isn't surprising considering that it's about a zombie apocalypse. If you want a non-comic-book example, the original French version of The Vanishing is true high octane nightmare fuel.
And if your beef is with that kind of entertainment well, then, I can relate. Battlestar Galactica is a very well put together show, but it's not something I could ever watch more than once. I felt crappy for several days after watching The Vanishing. All things considered, I do find that writers sometimes try to out-angst each other, to my occasional chagrin.
It's just that I don't lump the recent crop of naturalistic, believable movies into that category. Your mileage, of course, may vary. Hey, there's always The Avengers! :-)